Continuously variable transmission system

ABSTRACT

A multi-regime continuously variable ratio transmission has an output shaft ( 16 ), a variator and epicyclic gear sets (E 1,  E 2 ) arranged coaxially to provide drive to two coaxial output shafts ( 20, 26 ). The drive from the coaxial output shafts ( 20, 26 ) is selectively connectable to an offset system output shaft ( 22 ) by means of high-and low-regime clutches (H, L) arranged coaxially with the system output shaft ( 22 ).

The present invention relates to multi-regime, continuously variableratio transmission (CVT) systems, for example for use in motor vehicles.

A CVT system of this type is disclosed in EP-A-0149892. The systemdisclosed therein has the advantage of being “coaxial”, i.e. with thesystem input and output shafts, the CVT unit (variator) and the twoepicyclic gear trains being arranged coaxially, which has the advantagesof compactness and simplicity. However, the space available for locatinga transmission is often limited, particularly in smaller vehicles, andthe use of a coaxial CVT system may not allow the drive to betransferred easily to the driven wheels.

In accordance with the present invention, there is provided amulti-regime continuously variable ratio transmission system comprising:

-   -   a system input shaft;    -   a continuously variable ratio transmission unit (variator)        connected coaxially to the system input shaft and having a        variator output arranged coaxially with the system input shaft;    -   gearing means connected coaxially to the system input shaft and        the output of the variator and having first and second gearing        output shafts arranged coaxially with the system input shaft;    -   a system output shaft offset from the system input shaft; and    -   first and second clutches arranged coaxially with the system        output shaft to selectively couple the drive from the first and        second gearing output shafts to the system output shaft.

The provision of a variator and gearing means coaxially in combinationwith an offset system output shaft provides many advantages.

Firstly, the variator has all the benefits of reduced length, improvedcompactness, and improved stiffness associated with a coaxial designwhile at the same time the offset system output shaft allows output tobe taken from either or both ends of the shaft, which is particularlybeneficial for four-wheel drive applications. Secondly, the presentinvention allows a potential length reduction as compared with whollycoaxial designs.

In one embodiment, the gearing means comprises a first mixing epicyclicgear train having inputs driven by the system input shaft and thevariator and a first epicyclic output shaft arranged coaxialy with thesystem input shaft and forming the first gearing output shaft;

-   -   a second epicyclic gear train having an input driven by the        system input shaft and a second epicyclic gear train output        arranged coaxially with the system input shaft and forming the        second gearing output shaft.

Preferably the system output shaft is aligned parallel to the systeminput shaft.

In one embodiment, the first and second clutches are selectivelyconnectable to a common clutch output plate connected to the systemoutput shaft.

The drives from the first and second epicyclic gear train output shaftsare preferably transmitted to one side of the first and second clutchesrespectively.

Preferably, the first clutch is engaged to place the transmission in lowregime and the second clutch is engaged to place the transmission inhigh regime.

The invention also includes a motor vehicle comprising a transmissionsystem in accordance with the invention.

By way of example only, a specific embodiment of the present inventionwill now be described, with reference to the accompanying drawings, inwhich:

FIG. 1 is a diagrammatic illustration of an embodiment of continuouslyvariable transmission in accordance with the present invention; and

FIG. 2 is a diagram explaining the principles of operation of thetransmission of FIG. 1.

Referring firstly to FIG. 1, a continuously variable ratio transmissioncomprises a variator V of the known toroidal race rolling traction typehaving two toroidally-recessed discs 10 arranged one at each end of theunit and a pair of similar output discs 12, each facing a respective oneof the input discs 10 and rotating with each other. Sets of rollers 14are mounted between the opposing faces of the input and output discs 10,12 to transmit drive from the input discs 10 to the output discs 12 witha ratio which is variable by tilting the rollers 14.

The input discs 10 are connected to and driven by a system input shaft16. The variator provides an output via a tubular variator output shaft18 which is arranged coaxially with the input shaft 16. The end of theshaft 18 remote from the variator V drives the sun gear S1 of a first,mixing epicyclic gear train E1. The carrier C1 of the gear train E1 isconnected to, and driven by, the input shaft 16 and carries planet gearsP1 which mesh with an annulus A1 which is connected to a firstintermediate tubular output drive shaft 20 arranged coaxially with thesystem input shaft 16. The first output drive shaft 20 is selectivelyconnectable by means of a low-regime clutch L to a system output shaft22, which is offset from, but parallel to, the system input shaft 16, aswill be explained.

The sun gear S1, the planet gears P1 and the carrier C1 of the firstepicyclic gear train E1 also form the input sun, planet gears andcarrier respectively of a second epicyclic gear train E2. The spindles24 on which the planet gears P1 are mounted also each carry a furthergear P1′ at the opposite end, which meshes with an output sun gear S2connected to a second intermediate output drive shaft 26 arrangedcoaxially with the system input shaft 16 and within the firstintermediate output drive shaft 20. The planet gears P1, P1′ and/or thesun gears S1, S2 of the first and second epicyclic gear trains E1, E2,may be the same sizes (which would help to minimise cost) or differentsizes (to realise a change in output ratio). The second intermediatedrive shaft 26 is selectively connectable to the system output shaft 22by means of a high regime clutch H, as will be explained.

Thus, the coaxial arrangement of the variator V and the two epicyclicgear trains E1, E2 produces two coaxial intermediate output shafts20,26. The drive from the first intermediate output shaft 20 istransmitted from the shaft to one side 28 of the low regime clutch L bymeans of an output gear 30 located on the output shaft 20, an idler gear32 (which reverses the direction of rotation) and to a clutch input gear34 located on a tubular, low-regime clutch input shaft 36 arrangedcoaxially with the system output shaft 22.

The drive from the second intermediate output shaft 26 is transmittedfrom the shaft to one side 38 of the high regime clutch H by means of anoutput gear 40 located on the output shaft 26 and a high-regime clutchinput gear 42 located on a tubular, high-regime clutch input shaft 44arranged coaxially with the system output shaft 22.

By applying the low-regime or high-regime clutch L, H as required, thedrive from the first intermediate output shaft 20 or the secondintermediate output shaft 26 is transmitted to a common clutch plate 46which rotates with the system output shaft 22. Thus, the drive from thefirst or second intermediate drive shaft 20, 26 can be transmitted tothe system output shaft 22 by appropriate control of the clutches L, H.

The operation of the embodiment of FIG. 1 is illustrated schematicallyin FIG. 2.

The provision of a system output shaft 22 which is offset to a coaxialvariator/epicyclic gear train assembly (V, E1, E2) allows the systemoutput drive to be taken from either end of the system output shaft 22(for front- and rear- wheel drive vehicles respectively) or from bothends of the output shaft (for four-wheel drive vehicles) as may beappropriate, yet still offers many of the advantages afforded by thecoaxial variator/epicyclic gear train assembly.

The invention is not restricted to the details of the foregoingembodiment. For example, although the system output shaft 22 isdescribed as being parallel to the system input shaft 16, it may beappropriate to incline the system output shaft 22 to the system inputshaft 16, for example to suit the available space for the transmission.Furthermore, although the two clutches L, H are nested with each other(i.e. they are engagable with a common output plate 46), it may beappropriate to separate the clutches so that they are spaced apart alongthe length of the system output shaft 22.

Moreover, a variator other than a toroidal race rolling traction typevariator could be used. Moreover, although a two-regime transmission hasbeen described, the invention is equally applicable to three-orhigher-regime transmission, by selection of appropriate additionalepicyclic gearsets and regime clutches.

Also, depending on the required direction of rotation of the outputshaft 22 the idler gearset 30, 32, 34 can be used as described for lowregime output or alternatively could be used for high regime output,resulting in a reversal of the transmission output, in which case thelow regime output wouuld be taken through a conventional, non-reversinggearset.

1. A multi-regime continuously variable ratio transmission systemcomprising: a system input shaft; a continuously variable ratiotransmission unit (variator) connected coaxially to the system inputshaft and having a variator output arranged coaxially with the systeminput shaft; gearing means connected coaxially to the system input shaftand the output of the variator and having first and second gearingoutput shafts arranged coaxially with the system input shaft; a systemoutput shaft offset from the system input shaft; and first and secondclutches arranged coaxially with the system output shaft to selectivelycouple the drive from the first and second gearing output shafts to thesystem output shaft.
 2. A transmission system as claimed in claim 1,wherein the gearing means comprises: a first mixing epicyclic gear trainhaving inputs driven by the system input shaft and the variator and afirst epicyclic output shaft arranged coaxially with the system inputshaft and forming the first gearing output shaft; a second epicyclicgear train having an input driven by the system input shaft and a secondepicyclic gear train output arranged coaxially with the system inputshaft and forming the second gearing output shaft.
 3. A transmissionsystem as claimed in claim 1, wherein the system output shaft is alignedparallel to the system input shaft.
 4. A transmission system as claimedin claim 1, wherein the first and second clutches are selectivelyconnectable to a common clutch output plate connected to the systemoutput shaft.
 5. A transmission system as claimed in claim 1, whereinthe drives from the first and second gearing output shafts aretransmitted to one side of the first and second clutches respectively bymeans of gearing.
 6. A transmission system as claimed in claim 1,wherein the first clutch is engaged to place the transmission in lowregime and the second clutch is engaged to place the transmission inhigh regime.
 7. A motor vehicle comprising a transmission system asclaimed in claim
 1. 8. A transmission system as claimed in claim 2,wherein the system output shaft is aligned parallel to the system inputshaft.
 9. A transmission system as claimed in claim 2, wherein the firstand second clutches are selectively connectable to a common clutchoutput plate connected to the system output shaft.
 10. A transmissionsystem as claimed in claim 3, wherein the first and second clutches areselectively connectable to a common clutch output plate connected to thesystem output shaft.
 11. A transmission system as claimed in claim 2,wherein the drives from the first and second gearing output shafts aretransmitted to one side of the first and second clutches respectively bymeans of gearing.
 12. A transmission system as claimed in claim 3,wherein the drives from the first and second gearing output shafts aretransmitted to one side of the first and second clutches respectively bymeans of gearing.
 13. A transmission system as claimed in claim 4,wherein the drives from the first and second gearing output shafts aretransmitted to one side of the first and second clutches respectively bymeans of gearing.
 14. A transmission system as claimed in claim 2,wherein the first clutch is engaged to place the transmission in lowregime and the second clutch is engaged to place the transmission inhigh regime.
 15. A transmission system as claimed in claim 3, whereinthe first clutch is engaged to place the transmission in low regime andthe second clutch is engaged to place the transmission in high regime.16. A transmission system as claimed in claim 4, wherein the firstclutch is engaged to place the transmission in low regime and the secondclutch is engaged to place the transmission in high regime.
 17. Atransmission system as claimed in claim 5, wherein the first clutch isengaged to place the transmission in low regime and the second clutch isengaged to place the transmission in high regime.
 18. A motor vehiclecomprising a transmission system as claimed in claim
 2. 19. A motorvehicle comprising a transmission system as claimed in claim
 3. 20. Amotor vehicle comprising a transmission system as claimed in claim 4.